Superman reference of how high I keep stepping

Of course, Superman can fly, so Earl shows that he raps as well as Superman flies. With the word stepping, he could be walking up stairs, thus getting higher up off the ground, and rising to fame. And since Earl and most of the members of Odd Future smoke weed, he gets as high as Superman flies

“I keep stepping” might also be a reference to Christopher Reeve, the actor who played Superman, who was in a wheelchair at the end of his life.